1. Field of the Invention
The present invention relates to a communication system including a plurality of communication apparatuses. In particular, the present invention relates to a noise detection method, a noise detection apparatus, a simulation method, a simulation apparatus and a communication system which are capable of automatically detecting an impulsive noise, generated suddenly in a communication medium, from a statistical property of the observed noise itself.
2. Description of Related Art
Recently, in each field, there has been utilized a system in which a plurality of communication apparatuses are connected and functions are allocated to the respective communication apparatuses to mutually exchange data, thereby allowing the apparatuses to carry out various processes in conjunction with each other. In a communication system, the quality of communication is influenced by impulsive noises generated in a communication medium through which the communication apparatuses are connected to each other. Accordingly, it is necessary to take measures to prevent impulsive noises, or to realize communication so as not to be influenced by impulsive noises.
In the field of in-vehicle LAN (Local Area Network) provided in a vehicle, ECUs (Electronic Control Units) functioning as communication apparatuses are used, and the ECUs are allowed to carry out specialized processes to mutually exchange data, thereby realizing various functions as a system. Vehicle control is shifting from mechanical control toward electrical control, and specialization of functions of respective ECUs and functions realized by a system are on the increase. In accordance with this, the number and types of communication apparatuses are increased, and the number of communication lines through which the communication apparatuses are connected to each other is also increased. Further, with an increase in the amount of data received and transmitted by a communication system, it is necessary to receive and transmit a large amount of data at a higher speed.
In regard to this, attention is being given to PLC (Power Line Communication) for realizing communication by superimposing a communication carrier wave on an existing power line, and in addition, the application of PLC to in-vehicle LAN has been proposed (see Patent Document 1, for example). The application of an in-vehicle PLC system to in-vehicle LAN can achieve a reduction in the number of lines, thus making it possible to expect various effects including: a reduction in the weight of a vehicle; an improvement in fuel efficiency; and effective utilization of a space in a vehicle.
In an in-vehicle PLC system, data has to be received and transmitted with low delay and high reliability for safety reasons in particular. However, since an actuator is connected to a power line in in-vehicle PLC, a high amplitude impulsive noise is generated suddenly due to operation and/or suspension of the actuator. Therefore, it is necessary to: automatically detect the impulsive noise from a statistical property of the observed noise itself; conduct detailed preliminary studies on a communication method or the like effective for the impulsive noise that differs depending on a vehicle type or an option; and appropriately select a communication method, a frequency and a communication parameter.
As a method for detecting an impulsive noise, a method for detecting whether or not there is an impulsive noise based on an amplitude threshold and/or distribution of length of a given observation window (window size) has conventionally been used (see Non-Patent Documents 1, 2, 3 and 4).